The present invention relates to improvements in the alkylation of aliphatic hydrocarbons in the presence of a hydrogen fluoride catalyst.
Acid catalyzed alkylation of aliphatic hydrocarbons with olefinic hydrocarbons is a well-known process for the preparation of high octane gasoline products. Alkylation of hydrocarbons is industrially accomplished in the liquid phase by mixing paraffins and olefins in the presence of a strong acid catalyst and stirring the mixture until the alkylation reaction was completed.
To date the usually employed acid catalysts for industrial alkylation of aliphatic hydrocarbons are concentrated sulphuric acid or anhydrous hydrofluoric acid, the strength of which may be increased by addition of a Lewis acid, such as BF.sub.3 or SbF.sub.5.
Those batch processes require large reaction volumes and thoroughly mixing of the alkylation mixture by mechanical mixing means in order to provide intimate contact between the acid catalyst, the reacting hydrocarbons and the olefinic alkylating agent.
Although being very efficient, a major drawback of the known alkylation processes are the environmental and health risk involved during handling of large amounts of the above acids, as necessary in the processes.
Besides being hazardous materials, sulphuric acid and hydrofluoric acid are aggressive compounds under the reaction conditions used in the alkylation processes. At ambient conditions hydrofluoric acid is a volatile gas, which necessitates the alkylation process to be carried out at low temperatures or at elevated pressure.
Increasing concerns about the safety of HF-alkylation have caused some improvements in the alkylation processes using this acid including modifications using additives and changes in reactor design (WO 93/00315, WO 93/00316, U.S. Pat. No. 5,196,627, U.S. Pat. No. 5,196,628, U.S. Pat. No. 5,196,629, U.S. Pat. No. 5,114,675 and U.S. Pat. No. 4,938,935). Though those measures lower the vapour pressure and thus lowers the risk slightly, they do not solve the problem involved in handling large quantities of liquid volatile hydrogen fluoride, which in case of an accident can escape to the environment.